One prior-art method of affecting such folding of a sheet of foil involves running the sheet over the end of a roll in such a way that an edge portion of the sheet projects beyond the end of the roll. This initiates a fold in the foil at the end of the roll, causing the edge portion of the sheet to partially fold over toward the body portion of the sheet. Thereafter, a finger or roller is forced against the partially-folded edge portion of the foil sheet, thereby forcing the edge portion into a substantially fully-folded position with respect the body portion. The fold is set as the folded portion of the sheet goes over another roller. This technique is not as reliable as often required, does not always leave a clean fold, and has a tendency to pucker the edge of the foil sheet.
Another prior-art method of folding involves use of an appropriately shaped shoe which rubs against the edge portion of the moving foil sheet and forces the edge portion to fold up and over as the foil sheet moves ahead. A disadvantage of this method is that the rubbing relationship of the shoe on the foil sheet produces objectionable drag on the moving sheet and also generates dirt particles.